And fans who donate money to the cause will then get the chance to win a special drink - a bottle of water filled from taps at the stars' homes.
In one of the advertising posters highlighting the scheme, Rihanna poses next to a bottle of her personalised drink with the words, "Rihanna Tap Water. Not your typical tap water, unless of course, you live next door to Rihanna."
A message on the UNICEF Celebrity Tap website reads, "Celebrities have donated their own tap water to help raise awareness of the world water crisis. Donations enter individuals in our sweepstakes to win an esteemed collection of these famous tap waters."